In the analyzer shown in U.S. Pat. No. 4,296,070, FIGS. 2-4 especially, two different slide blocks or holders 40 are provided to hold a test element or slide 15 or 17. One kind of slide 15 is a colorimetric test element, with a liquid-receiving area that is centered, FIG. 3. The other kind of slide 17 is a potentiometric test element with a sample liquid-receiving area that is offset from center. Also featured in the holder is a tip locator, unnumbered, shown as a vertically rising cylinder or turret, in FIG. 4. That tip locator is used to locate the dispensing tip from the metering tower 18, FIG. 2, relative to the slides, to permit liquid dispensing onto the slides. The holders 40 are rotated into position under the tower by rotation of rotor 32, FIG. 3, that mounts holders 40 at the ends of arms 36. As is evident in FIG. 3, the tip locator is slightly off-center for holders designed for slides 17, compared to the tip locator that is precisely centered for the holders designed for slides 15. Thus, each slide holder is dedicated to one type of slide or the other. Such dedication requires, among other things, a more complex software and timing program in order to keep track of which slide holder is appropriate for which kind of assay.
What has been needed prior to this invention is a universal slide or test element holder that will allow either type of slide to be held, and at the same time accommodate either the centered dispensing for slides 15, OR the offset dispensing for slides 17. The simplest procedure for doing that is of course to modify the tip locator so as to have two vertical passageways, each slightly offset relative to the other, so that a dispensing tip can be brought down to the center of a slide (if colorimetric), or to one side of center (if potentiometric). However, I discovered that a problem exists if this is done--the standard opening for the tips causes considerable overlap of the side-by-side passageways. This overlap gives incomplete positive location of the dispensing tip in the X-Y plane, and is unacceptable. Yet at the same time, such standard-sized opening has been needed to accommodate the dispensing tips used. It would be unacceptable to make such tips smaller overall to overcome that problem, for several reasons. Not the least of these reasons is that the molds used to mold the tips would have to be redesigned.
Therefore, there has been a substantial need to provide a universal slide holder for receiving in the analyzer either a colorimetric or a potentiometric slide, without requiring a redesign of the dispensing tip that cooperates with the slide holder during liquid dispensing.